Herein, a single luminophor dual-potential chemiluminescence (ECL) system based on nitrogen doped graphene quantum dots (NGQDs) was developed for ratiometric detection of Co2+ ion. Dissolved oxygen is changed to O-2(center dot-) and HO2- which participate in the anodic and cathodic ECL generating processes of NGQDs. Co2+ ion was demonstrated able to evidently amplify the anodic intensity by displaying catalytic action of the intermediate steps of anodic ECL reactions, and quench the cathodic ECL intensity because of the effective elimination on excited states (NGQDs*) generating. Hence, the target Co2+ ion could be quantified by the ratio of ECL intensities at two excitation potentials. On this basis, without any labeling and additional coreactants, an accurate and reliable sensing system based on the dual-potential ECL of NGQDs toward Co2+ ion was fabricated with excellent sensitivity and selectivity against other interferential metal ions. The developed ratiometric sensor exhibited a linear response ranging from 1.0 mu M to 70 mu M with a limit of detection of 0.2 mu M (S/N = 3). The proposed dual-potential ratiometric NGQDs based ECL sensor was also used to detect Co2+ ion in real water samples. As single luminophor, NGQDs possessing multiple-ECL signals is simple without labeling, providing more reliable signals in sensing than other essential state dependent techniques. (C) 2016 Elsevier Ltd. All rights reserved.